Hello, collective wisdom and well of overheard conversation.
Please save me from doing this again: hanging on hold with the cable company again, only to be told to leave a message for someone in engineering, who does not return the call.

Can anyone out there tell me what frequencies are used for the digital cable signals? In particular, the cable system around here (Los Angeles) is Adelphia.

Some of my clients have camera or DSS signals modulated onto previously unused cable channels. What happens now? Is digital above the regular cable channels? I know I will have to pass the modulated signals around any cable boxes in use, but those signals will not be able to be used on the same frequencies as the digital channels, box or none.

I saw this previously when some customers with outdoor antennas lost modulated signals when DTV signals started to be sent out on the UHF frequencies I had used.

So, any ideas or facts out there?

I don't often get the chance to visit here, so please share with everybody on this forum, and also email me if you can.

Thanks --

Ernie
[email protected]

This is an excellent question! I live in Florida but we were faced with this same dilemma over a year ago when digital cable boxes started being installed.

The cable company here (Cox) told us that there is no empty bandwith space to inject a modulated signal for a digital cable box location. They said we would have to get a notch filter and remove a channel that the customer does not want anymore, but these tight filters are very expensive.

The only solution we have been using is that usually the only TV that gets the digital cable box is the theater area where we have extra cables. We send the raw composite video from the camera to the theater area and have the TV go to the video mode that this signal is plugged into to view it.

The other regular TV's can still have the signal modulated as normal. You just have to make sure that you split the incoming cable; one side feeds directly to digital cable boxes (unmodulated) and the other side to your cable distribution block to the regular TV's that contain the injected modulated signal (since for regular TV's you have no use for the digital cable signal and you can filter it right off).

I would love to hear from others who are dealing with this problem.

Jeff

This message was edited by Jeff406 on 04/09/02 20:27.36.

I dealt with a similar situation in the San Francisco area.All the channles under 110 I beleive are regualr analog and the channels above are all digital. What we did was notch out some of the higher channels under 110 that the customer didn't watch and then modulated onto them. They were even able to still view these channels through their cable box.

Channel Plus makes a piece for systems with cableboxes.



To bypass a UHF station around a cable box.
When a cable operator requires the use of a set top box but there are no channel vacancies to create a ChannelPlus channel, create a UHF channel and use C-BCK on all TVs that have a set top box. View the cable box on channel 3 and the modulated channels on their UHF channel numbers.



JJP


This message was edited by John Pechulis on 04/09/02 20:58.36.

Here in Upstate NY (TimeWarner Land) I modulate to channels 125 and up. It works well if there is no old TVs in the house.

John

digital cable is usually in the 550 to 750 mhz range, the above solutions work if you are dealing with addressable cable boxes

Just a note: Im my area, they are using the Channel range for 79-85...we also have cable modem problems that range in the ch. 111 to 114. I'd say stay in the 120's and you'd be fine. Also, you can hook up a base tv to the cable and scan the channels. If you see group of 3 channels with no noise on 'em, insert on the center channel...

Many thanks for your responses. This helps. And sort of to recap --

I love the idea of switching the TV to UHF when it is used with a cable box. This gives us up to UHF 69, 801.25 MHz, for modulation (I have not checked how high modulators actually go).

DBDElectronics says “digital cable is usually in the 550 to 750 mhz range....”
Just to flesh that out, that means UHF 27 to 60, cable 79 to 117....

Jwalkup says “Here in Upstate NY (TimeWarner Land) I modulate to channels 125 and up. It works well if there are no old TVs in the house.”
Okay, using frequencies above 117 mentioned above. But I have not seen any channels over 125; in fact, the latest list I have seen only goes to 116 (745 MHz).

Any more info out there?

Thanks,

Ernie

I got a response by email from someone who apparently does not have a password (see THAT string for some vitriol!!). Here is his reply, without attribution because I do not have the time to clean up the grammar etc. The data here backs up the earlier frequency and channel claims:

I think i can help with your problem having worked for some of the karger cable cos. Dig box freq start at about 750 mhz and go up from there. As far as modulation goes that is a common problem now you have to stay above ch # 116 at a minimum now if you brodcasting like comcast is at that freq you have to go higher like to 120 and up. Now if you dont have a dig box on all tvs you can splitt the dig box off from the rest of the system then use a low or high pass filter to work around the modulatrion problem. You can also run a modulated signal through a cable box by activating the rf bypass in the cable box menu.What type of boxes are they using GE, SA, PIONEER ? Feel free to e-mail me with ant more questions regarding this matter.

I just finished a job with similar problems. The best results were obtained modulating the DVD to channel 120 and the VCR to channel 125 with an HMM-10 modulator.

I sent you the e-mail sorry for the grammer cant type very well sometimes. I have worked for Time Warner,Comcast,Inter-Media,Charter and a few others all the information you have is correct if you stay above ch#118 on your modulation you will be ok try to keep your signal levels close to each other or you will find a harringbone effect on your channels in the 30-40 range.Dont forget to check in your cable box menu for the rf bypass that will allow the modulated channels to pass through the cable box. T.W.,Comcast,and Charter I know all use the same Digital boxes.The other scenario is with ant. you can usually modulate above ch # 45

One more question that I have is, are you all using filters to filter out the bandwidth before you modulate a signal on it, and if so, where are you finding filters that filter out channel 117 and above?

This has been interesting for me, since our cable company said they are using all available bandwidth and there is no where to modulate a signal, apparantly they were wrong.

Jeff